Comparison of alfalfa and mixed alfalfa-sainfoin pastures for grazing cattle: Effects on incidence of bloat, ruminal fermentation, and feed intake

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Grazing experiments were conducted over two years to evaluate the effects of incorporating sainfoin (Onobrychis viciifolia) into alfalfa (Medicago sativa) pasture on bloat, ruminal fermentation, and feed intake. Pastures of alfalfa (Alf) and alfalfa-sainfoin (AS) were established by cross-seeding (in 1998) or parallel-seeding in (1999) sainfoin into strip-seeded alfalfa. The pastures were used in grazing studies in 1999 and 2000. For periods of 4 or 5 d, 12 ruminally cannulated Jersey steers were turned out into pastures from 0830 to 1430 daily (without access to water) then were moved to a fenced area (with free access to water but no feed) until the next morning. Feed intake during grazing was estimated using alkane markers, development of bloat was assessed, and ruminal fluid (RF) fermentation properties were determined. Incidence of bloat on first-growth pastures grazed at early bloom in 1999 was unaffected by sainfoin (at 8.3%, DM basis) but was reduced by 80% (P < 0.001) in AS pasture compared with Alf, when grazed at full-bud in 2000 (12.1% sainfoin). With re-growth forage, bloat incidence was decreased by 77% (P < 0.05) on pasture containing 35% sainfoin, but treatment effect was not observed on pastures containing < 23% sainfoin. Incidence of bloat was reduced as the proportion of sainfoin in herbage mass increased. In 2000, ruminal ammonia concentrations were reduced (P < 0.05) with mixed forage containing ≥ 12.1% sainfoin, compared with Alf. Protozoal numbers, RF viscosity, and total volatile fatty acids (VFA) were unaffected by sainfoin in the forage, but acetate:propionate ratios were consistently reduced (P ≤ 0.036). Extracellular polysaccharide-degrading enzyme activities in RF were increased (carboxymethylcellulase and β-glucanase, P ≤ 0.034; xylanase, P = 0.008 and 0.08) by sainfoin at ≥ 12.1%, and proteolytic activities (intracellular and extracellular) were reduced (P ≤ 0.01). Enzyme activities were unaffected by sainfoin at ≤ 9.1%. Sainfoin did not affect (P ≥ 0.202) organic matter intake from any of the pastures surveyed. Sainfoin was more effective for reducing bloat when cattle were grazing first growth pastures than when grazing re-growth. Including 35% sainfoin in mixed alfalfa-sainfoin pastures reduced, but did not eliminate, bloat in beef cattle and enhanced protein utilization by decreasing proteolytic activity. Feed efficiency may be improved through associative effects of the two forages. Key words: Alfalfa, beef cattle, feed intake, grazing, pasture bloat, sainfoin